1. Field of the Invention
The present invention relates to improvements in automated methods and apparatus for aspirating liquids from containers, and/or for dispensing liquids into containers. More particularly, this invention is directed to improvements in methods and apparatus for minimizing (a) the inadvertent introduction of air into an aspirated liquid, and/or (b) the overfilling or non-filling of a container by a dispensed liquid.
2. The Prior Art
In automated analytical laboratory instruments, it is common to selectively mix together various reagents and sample materials in a mixing chamber in order to study, for example, the effects of such reagents on the sample material. Typically, in automated, high-throughput, instruments designed to repetitively perform various tests on a multitude of samples presented to it, the reagents (including sample diluents) are contained in relatively large containers or reservoirs that are stowed within, or adjacent to, the instrument housing. Such containers usually carry a cap through which a liquid-aspiration line or conduit passes that serves to gain access to the contained liquid. A syringe pump or the like operates to transfer a predetermined (relatively small) volume of the contained liquid to a desired location (e.g., the inlet of a mixing chamber) within the instrument. To avoid the aspiration of any air from the liquid container during the liquid aspirating process, it is essential, of course, that the free or distal end of the aspiration line be maintained below the level of liquid in the container. Any air introduced into the aspirated liquid will lead to erroneous test results since it compromises the provision of prescribed volumes of liquid required for a given test. Thus, to assure that the end of the aspiration line is safely below the liquid level in the container, it is common for the container cap to support a float switch or some other liquid level-sensor that serves to activate an alarm when the liquid level drops below a preset minimum value within the container, typically when the distal end of the aspiration line is just below a safe level. When an alarm occurs, the instrument operator must replace the nearly empty container with a fresh container of liquid and then attach the aspiration line-supporting and level-sensing cap to the new container.
In instruments of the above noted type, it is also common to dispense the liquid waste products from all the tests conducted within the instrument into a relatively large waste container located within or near the instrument housing. Here again, the cap of such container commonly supports a conduit or dispense line through which the waste liquid can enter the container. To assure the container is not overfilled, which could result in contaminating the laboratory area with a bio-hazardous liquid, the waste container cap also supports a float switch or the like that activates an alarm when the liquid waste level exceeds a predetermined safe level. When such an alarm occurs, the instrument operator will remove the nearly full waste container and replace it with an empty container, being certain to attach the dispense line and level-sensing cap.
In liquid aspirating and dispensing systems of the type described, there is always a possibility that the instrument operator, in changing reagent or waste containers, will not properly attach, or even forget to attach, the aforementioned aspiration/dispensing cap to the top of the new container. Note, when changing containers, the caps can be set down in an orientation in which the float switches which, upon being removed from the liquid, are free to assume either an OPEN or CLOSED state, will mistakenly indicate to the instrument logic that the liquid level is within a safe limit. When the caps are not properly attached to their intended container, air can enter the aspiration line, or waste liquid can leak from the waste container or even be dispensed outside the container.